With the recent development of multimedia, demands for recording various types of multimedia data such as movie pictures, music, still pictures, onto recording media have increased. Among such recording media, tape media such as video tape and audio tape were widely accepted in the past, but in recent years, disk media such as hard disks, magnetic disks and the like have become prevalent to store data.
Tape media are recording media with which recording and reproduction of data is performed sequentially from the top of the tape, i.e., by sequential access, so that they are poor in random accessibility. For example, if with a video tape, playback from a specified position is wanted, the tape needs to be advanced by fast-forward or rewound by the rewind function to adjust the designated position before reproduction.
If some index information indicating the target position has been set beforehand, the access can be implemented by simply searching the index but still needs the physical operation of moving the tape to the target position. If no index information is provided, it is necessary to locate the target position by implementing fast-forward whilst playing back in order to locate the target position, or it is necessary to implement approximate fast-forward adjustment using guesswork and final location of the target by playing back in order to obtain access to the target position. In the above way, tape media, if they are used, are not suitable to random access because they need physical tape movement.
In contrast, disk media are excellent in random accessibility, and the access time to an arbitrary location is negligible compared to that of tape media. That is, wherever data is on the disk, it is possible to have an access instantaneously.
As typical utility examples of disk media, MD is known for audio and DVD is known for video, these are widely spread because of their random accessibility.
Now, a case where video data encoded by the MPEG format is recorded on to a disk will be described. For recording video data onto a disk or for transmitting it via a transmission line, it is not practical if the video data is directly transmitted without being compressed because the amount of data is too bulky. Therefore, it is necessary to compress video data to reduce the amount of data by using the MPEG technique or the like.
In the MPEG technique, in compressing the amount of data, the variable-length coding technique is used. Specifically, video data is efficiently reduced in its amount using three types of image compression, namely the intraframe coding picture(I-picture) which is encoded independently using the data within that video frame, the interframe forward predictive coding picture(P-picture) which is encoded based on the information of the previous frame and the bi-directional predictive coding picture(B-picture) which is encoded based on the previous and subsequent frames.
Of these encoded pictures, the compression ratios become higher in the following order, I-picture, P-picture and B-picture. Therefore, depending on the encoding picture type, the amount of data for one frame of video differs from that of another while the amount of data also differs depending on the content of the original video data. For example, if video data has less motion, the P-picture and B-picture little differ from the associated I-picture so that the data can be compressed markedly efficiently.
Illustratively, the amounts of data for individual frames of video data are different as shown in the recording sequence(on the disk) in FIG. 64, and there is no means by which it is possible to compute the amount of data of each frame of MPEG data which has been once encoded, without implementing actual decoding of the MPEG data.
In the case where MPEG data which has been variable-length coded is recorded, the amounts of data for individual frames are different, therefore, it is impossible to grasp where MPEG data corresponding to each frame has been recorded on the disk until the recorded MPEG data is read out from the start of data and decoded sequentially.
In other words, if reproduction is wanted to start from an arbitrary point in the recorded MPEG data, the data cannot be played back from such a partway point because the position on the disk where the MPEG data, which corresponds to the frame from where the start of playback is wanted, has been recorded cannot be known.
Therefore, in order to play back the MPED data recorded on the disk from an arbitrary point, or in order to implement special playback using arbitrary frames, it is necessary to obtain management information for managing the data record positions on the disk corresponding to individual frames. Using this management information, it becomes possible to refer to the recorded location of an tributary frame on the disk.
Also, as stated already, MPEG data is efficiently reduced in amount of data by using three types of image compression, namely the intraframe coding picture (I-picture), interframe forward predictive coding picture (P-picture) and bi-directional predictive coding picture(B-picture). Since the P-picture and B-picture is generated based on the associated I-picture, it is impossible to decode that data only.
No problem will occur when MPEG data is decoded and played back serially from the front, but when MPEG data is played back from a frame partway in the data or when special playback by picking up arbitrary frames is implemented, the following problem occurs. That is, if the frame from which the start of playback is wanted is a P-picture or B-picture, it is impossible to decode the frame without the I-picture and/or P-picture data based on which the frame in question has been constructed.
To deal with such a situation, the MPEG scheme has a structure called GOP (Group of Pictures) made up of a number of frames. This GOP structure is featured by inclusion of at least one I-picture in one GOP.
Accordingly, if each GOP structure is assumed to be the access unit, the GOP necessarily includes the I-picture based on which P-pictures and B-pictures have been constructed, so that decoding of the target frame can be assured.
In this way, for realizing random access to MPEG data, the access should be made to each GOP structure by assuming it to be a unit. For example, even when the start of playback is wanted from a frame partway within a GOP structure, the control of the playback should be performed such that the whole data of the GOP is decoded first, then actual display may be started from the target frame. This produces the same result as if playback were merely started from target frame.
As described above, in order to start playback from an arbitrary frame within MPEG data, it is necessary to at least have positional information on the disk of the GOP that includes target frame, instead of positional information on the disk of each frame.
That is, in the case where positional information of all the frames is given as management information, if the data of the frame from which the start of playback is wanted is a B-picture or P-picture, the frame of data from which the start of playback is wanted has little meaning because the data cannot be decoded unless the data of the I-picture used as the reference.
On the other hand, for a case of special playback such as fast-playback in which only I-pictures and P-pictures are reproduced, the positional information of I-pictures and P-pictures on the disk is needed.
As one prior art for recording MPEG data onto disk media, there is the read-only type DVD. In DVD, video data constituting one GOP and audio data associated with it are multiplexed with a piece of management information called a NV (Navigation) pack added to the front of the data.
Use of NV packs as the information for implementing special playback makes it possible to grasp the positions at which the next and previous NV packs have been recorded on the disk, with respect to the site being currently played back.
Japanese Patent Application Laid-Open Hei 11 No.155130 discloses an example of the address management information when MPEG data is recorded into rewritable media. According to this disclosure, the address management information is configured of time map information including a VOBU (Video Object Unit) map presenting the address of each VOBU as one management unit in the MPEG scheme in association with time information, address information offering the addresses of the VOBUs to be reproduced at intervals of a fixed time period and identification information for identifying each VOBU.
Usually, in rewritable recording media, since some MPEG streams may be deleted or moved on the disk, the management information or the like could be changed disorderedly. In the case where the management information is changed disorderedly, the system response will be improved if the management information can be read or written by a single access.
However, for the aforementioned DVD, management information is constructed on the assumption of ROM media, the management information is multiplexed within the MPEG stream every NV pack so it is scattered in pieces on the disk. Accordingly, to update the management information, it is necessary to make accesses to pieces of the management information scattered on the disk, one by one, which is unfeasible.
Further, an access to the MPEG stream assumed to be made in the above disclosure described in Japanese Patent Application Laid-Open Hei 11 No.155130 is implemented by unitwise—VOBU random access. In this case, the number of video frames to be managed by a single VOBU is variable.
In other words, the playback time corresponding to one VOBU is variable, so that when a certain frame is tried to be designated by time information, a search of the VOBU including that frame wanted to be reproduced cannot be made by a simple calculation. In this case, it is necessary to locate the VOBU by checking the playback period of time of each VOBU one by one sequentially from the front VOBU, for example.
When the target VOBU is located within a short distance from the front VOBU, it does not take much time for searching, but when the target is located some distance from the front, it takes much time to search it. To deal with this, in this disclosure of Japanese Patent Application Laid-Open Hei 11 No.155130, other than the VOBU map information for managing addresses of all VOBUs and time information, the time map information indicating VOBUs corresponding to the addresses of the VOBUs to be reproduced at intervals of a fixed period of time is used.
That is, for searching the VOBU containing a target video frame, the time map information should be referred to first before access to the VOBU information is made. Further, the VOBU map information searched based on the time map information does not always hit the VOBU containing the target video frame, VOBU information following the searched VOBU information needs to be searched serially until the target VOBU is found.
As above, since in the prior art, to search the target video frame, a rough search is made first using the time map reference information then an exact search is performed using the VOBU information to thereby identify the corresponding address on the disk, the prior art has the problem of such complicated process being needed.
Moreover, when post recording such as audio dubbing, superimposition of images, etc., is added, post recording units(PRUs) for securing areas for this post recording information within the MPEG stream or separately outside the stream need to be defined in the stream. However, the above described prior art cannot deal with such streams.
The present invention has been devised in view of what has been discussed above, and it is therefore an object of the present invention to provide a recording media management system, including the method of locating access positions in a recording medium and managing device of the recording medium, which is able to determine the address of a target video frame in a simple manner and is adapted to deal with streams having PRUs defined therein.